Abstract : The concept of treating planets as members of a general class of non-self luminous objects is introduced. Planets are shown to occupy the mass range roughly between 0.00001 to 10,000 earth masses (10 to the 23rd to 32d grams), objects above this mass range being stars and below this mass range being classified as meteoroids or asteroids. Planets are further classified into types as: (1) airless bodies; (2) planets with light atmospheres and (3) planets with massive atmospheres, the type being dependent on surface escape velocity and exosphere temperature. Some relationships among fundamental properties of planets are discussed: mean density vs. radius; atmospheric composition as a function of exosphere temperature and velocity of escape; and oblateness as a function of rotational velocity, mean density and internal density distribution. Some unresolved problem areas of general planetology are indicated. (Author)